The present invention relates to an electronic scanning type non-destructive testing apparatus which detects defects inside a structural member and displays the result of the defect detection.
The conventional ultrasonic non-destructive testing apparatus of this type, in the transmission mode, radiates ultrasonic waves by a plurality of transducers and focuses those waves into a single ultrasonic beam, which is transmitted in a desired direction on the basis of the principle of the phase interference of the ultrasonic waves radiated from the plurality of transducers through a control of the radiating timings of the ultrasonic waves. In the reception mode, the ultrasonic non-destructive testing apparatus receives ultrasonic echoes by a plurality of transducers, adds together the echo signals after a proper control of the delay times of the echo signals, and displays the added or intensified echo signal representative of the focused ultrasonic beam. The ultrasonic non-destructive testing apparatus is very useful because a tomogram of the member under defect inspection, viz. a B-scope image, is displayed in real time.
For a image display, the conventional ultrasonic non-destructive testing apparatus has employed a tonal display based on a strength or an amplitude of the echo signal or a bilevel display by setting up a level for discriminating an amplitude of the echo signal. For detecting size and configuration of a defect inside a structural member such as a metallic member, it is very important to accurately detect the location of the defect, and an amplitude, a waveform, and the like of the echo signal from the defect. The display method now employed, such as the tonal display or the bilevel display, does not provide an satisfactory accuracy in displaying the amplitude and the waveform of the echo signal.
The standard of ASME (American Society of Mechanical Engineers) requires the following judgment on the inspection of the defect in a structural member using a calibration block. An amplitude attenuation of the echo reflected from an actual member is corrected on the basis of an amplitude of the ultrasonic echo from a reference defect artificially formed in a reference member. An amplitude variation (amplitude attenuation) characteristic of the echo over the entire beam propagating path is obtained from the judgement through this correction work.
The conventional correction of the ultrasonic beam propagating path, as disclosed in U.S. Pat. No. 4,043,181, uses the amplitude characteristic of the received echo in the direction of only one ultrasonic beam propagating path for the attenuation correction of the echoes in every direction. Therefore, this correction method can not cope well variations in the amplitude characteristic of the ultrasonic beams in those different directions, resulting in degradation of the accuracy of the displayed image.
For the above reasons, it has been desired that the amplitude attenuation of the received echo signals in all the directions is accurately corrected, so as to ensure an exact display of an image of the inside of the structural member under defect inspection.